1. Field of the Invention
This invention resides in the design and use of temperature control blocks for use in multi-well reaction plates, such as those used in PCR procedures.
2. Description of the Prior Art
Certain chemical syntheses involve the use of sequential reactions, cyclic reactions, or multiple reactions occurring simultaneously. Prominent examples of such syntheses are the polymerase chain reaction and the ligase chain reaction. The polymerase chain reaction (PCR), for example, entails a sequence of steps including denaturing a polynucleotide, annealing primer oligonucleotides to the denatured polynucleotide, and extension of the primers to synthesize new polynucleotide strands along the denatured strands. The success of the procedure relies on high yield, high selectivity, and a controlled reaction rate at each stage. Yield, selectivity, and reaction rate often vary with temperature, and optimal temperatures in each case vary with such parameters as the length and nucleotide composition of the polynucleotide, and the choice of enzymes and other components of the reaction system. Determination of the optimal temperatures and accurate control of the temperatures at the optimal levels are important in achieving success in these procedures. Other protocols and procedures involve multiple reactions performed simultaneously in individual reaction vessels all at the same temperature. Accuracy and control are important in these procedures as well.
Laboratory apparatus in which this kind of control is achieved is offered by numerous suppliers. The typical apparatus includes one or more temperature-controlled blocks, each containing reaction wells in a two-dimensional array, with robotics to move samples between wells in a block or between different blocks and automated processing to control the temperature and drive the robotics. Examples are the RoboCycler 96 of Stratagene, the PTC-100 Thermal Cycler of MJ Research, the Perkin-Elmer DNA Thermal Cycler, and the DNA Engine Thermal Cycler of MicroPROBE.
Temperature control over the entire array of reaction wells in a two-dimensional array is often less than complete, and edge effects often arise, i.e., temperature differences at the outer wells due to their greater exposure to the atmosphere or to other instrument components. Also, temperature gradients along the well array, which would permit reactions at different temperatures or different protocols to be performed simultaneously, are difficult to achieve.
Also lacking from the units named above and similar units are features that permit the user to visually or optically observe the well contents during the course of the reaction and thereby achieve real-time detection of the progress of the reaction, and to enclose the wells with lids to prevent evaporation of the reaction mixtures without experiencing condensation on the undersides of the lids.
The present invention resides in part in a temperature block that can establish either a temperature gradient across an array of reaction wells or a uniform temperature throughout the array. The temperature block is useful as a component of a thermal cycler or other similar automated laboratory apparatus which also includes other components and features that participate in sample handling and the performance and control of multiple and/or sequential chemical reactions. One of the features of the block of the present invention is a unique ability to heat and otherwise control the temperature in all wells of the array while eliminating edge effects, i.e., temperature deviations in wells positioned either in the center of the array or along the outer edge of the array due to differences in heat dissipation in these regions.
The present invention also resides in a thermal cycler or similar multiple reaction apparatus that includes a heated transparent lid. The lid performs several functions. One is to apply force to enclosures that are placed over the tops of the wells to secure the contents of the wells from evaporation or other loss. Another is to press the wells down against the heating or cooling block positioned underneath the wells to achieve good thermal contact. This can be done without the use of oil which has been previously used for this purpose. A third function of the heated transparent lid is to permit sufficient light to pass and thereby permit the user to directly detect the progress of the reactions that are taking place in the wells. A fourth function is to prevent condensation of vapors on the undersides of the well enclosures, the condensations otherwise tending to introduce variations in the compositions of the reaction mixtures. The vapors are generated in the wells by the components of the reaction mixtures, particularly when the wells are heated from below.
These features of the heated transparent lid are particularly useful when the thermal cycler or multiple reaction apparatus is used for polymerase chain reactions. The lid is also useful for multiple reaction systems in general, both those in which the reactions are performed simultaneously and those in which they are performed sequentially.